There is a good thread on the topic here. There is a benefit to upvoting your comments (not your posts) that someone pointed out, which is that it helps put it higher in the order of other comments. If you feel that your comment has a lot of value to the post and should be seen, then it doesn't seem super selfish to try and get it higher.
Upvoting your own posts is a little different though. The only purpose of that is to make more SP/SBD for yourself.
https://steemit.com/upvote/@timcliff/opinion-why-you-shouldn-t-upvote-for-yourself